1. Field
Embodiments of the invention relate to electronic devices, and more particularly, in one or more embodiments, to configurations of bias circuits.
2. Description of the Related Technology
Biasing is a method of establishing particular electrical conditions at various points in an electronic circuit in order to set a desired operating point for one or more electronic devices included in the circuit. In particular, biasing is typically used to set and control a desired operating point for an active electronic device, such as a transistor. For example, a transistor can be controlled to provide various functions, at respective operating points, by establishing particular direct current (DC) bias conditions at the terminals of the transistor.
Bias conditions are commonly generated within the immediate vicinity of the active circuit and/or active device in need of biasing. In an effort to reduce component count and size a bias circuit is often integrated into the design of an active circuit. As a result, an active circuit is typically provided together with a respective custom bias circuit.
On an integrated circuit (IC) die or chip, the available space for circuits is limited. There is also a commercial preference to maintain or reduce the size of chips in order to increase semiconductor manufacturing yield, even as transistor density increases. Bias circuits detract from the amount of space available for the active circuits that perform the desired functions a chip has been designed for. Bias circuits also consume power that contributes to the heating of a chip, which can lead to performance degradation and even failure. Accordingly, as the demand for on-chip functionality increases, there lies a challenge to implement more complex circuits that consume less power and occupy less on-chip area.
Bias circuits are also typically designed with passive electronic elements in order to minimize the amount of power consumed. However, the output of a passive bias circuit will almost always change in response to changes in the voltage supply level. Such changes will in turn change the operating point of the active circuit receiving the bias. For example, the output of an amplifier may lose dynamic range (i.e. amplitude compression) if a bias voltage decreases in response to a decrease of the voltage supply level. One known solution to this problem is to provide a number of respective bias circuits that provide respective outputs that can be selectively coupled to an amplifier to produce the desired operation. The range of operating conditions over which this technique is useful is limited by the number of bias circuits that are provided. However, each additional bias circuit takes up additional space, which can be undesirable for on-chip applications, where die area is relatively expensive.